The banknote processing device is described, for example, in international application WO 00/46758 (published on Aug. 10, 2000, IPC G07D7/04). The device automatically scans a banknote and obtains its digital scan consisting of two-dimensional images of both sides of the banknote in the visible and infrared bands, and under ultraviolet radiation. The device is equipped with a computing unit for computational processing of the scan.
In compliance with the method used in the given device, characteristics of the banknote being analyzed and the reference one of the specified class are compared. To make this comparison, several square areas are allocated on the banknote two-dimensional digital image, and a set of statistical parameters for each area is calculated. Then the function of state is calculated for each area on the base of the set of statistical parameters; the more similar the given area is with the reference banknote, the higher the function value is. Then the number of areas with the function of state exceeding the specified threshold is counted, and a conclusion about the banknote class is drawn basing on the obtained result. If the number of such areas is higher than a certain minimal quantity, the banknote corresponds to the specified class. Further authenticity verification is carried out by making comparison of the list of areas where specified threshold was exceeded, and a mandatory list of areas.
The main imperfection of the method described in the above-mentioned application is a high computational costs for banknote processing. If a presupposed class of the banknote is unknown, its identification requires comparison of the banknote's digital image with a full set of reference banknotes of the classes to which the banknote being analyzed may correspond. A large amount of calculation is made in a course of comparison with each of the references, and the decision about the banknote membership is taken upon completion of these calculations. A large amount of calculations made for each banknote being analyzed results in high performance requirements applied to computing unit of the device. To ensure the processing speed, the computing unit shall have high performance. If it is low, the banknote processing speed is low.
This method is characterized by a practically linear increase in the performance requirements for the device computing unit with the rise of the number of classes the banknote may belong to. It is due to an independent checking of the banknote correspondence to each possible class. Therefore, to implement the given method, it is difficult to develop a device that would work with a considerable number of currencies of various countries.
The international application WO 2007/068867 (published on Jun. 21, 2007, IPC G07D7/20) discloses the essence of the banknote validation method. In compliance with the above-mentioned method, an automatic validation uses a set of one-class classifiers; each classifier is applied to a set of the features obtained from the banknote image. The classifier of one class is a computational process with an estimate statistical characteristic as its result. Each known class has a criterion of banknote membership in the specific class; the criterion is based on comparison of the values of an estimating statistical value for the given class with a predefined threshold value. In accordance with this method, classifiers for all known classes are applied to the banknote image, and only then their results are analyzed, and a conclusion is drawn about the banknote membership in some class. Drawback of the given method is that the main computational processing i.e. application of classifiers for each banknote is carried out in the same volume, and only then the result is analyzed. Imperfections of this solution are similar to the ones described before and pertinent to the method in application WO 00/46758.